This invention relates to a hydraulic motor with axial pistons.
In general, hydraulic motors of the aforesaid type comprise a plurality of pistons slidably mounted in respective cylinders provided axially through a rotor which is disposed in a casing and is keyed on to a central exit shaft. The said rotor is caused to rotate by a hydraulic fluid which acts at any time on one end of some of said pistons, urging them so that they press with their other end on a plate inclined to the axis of the rotor and generally constituted by a toroidal member rotatable about an axis and rotated by friction forces arising from contact with said pinions.
Although the aforesaid hydraulic motors are particularly efficient and are preferable in some applications to many other types of motor because of their ability to develop a relatively high specific power at a relatively low r.p.m., they suffer from certain drawbacks, the most important of which is their relatively short life. This drawback derives mainly from the fact that the forces which are exchanged between said toroidal member and each piston at their point of contact are generally parallel to the axis of the toroidal member. Consequently, the force with which the toroidal member acts on each piston produces a component transversal to the axis of the piston, which acts on this latter to cause it to preferentially rub against a generating line of the respective cylinder. This imperfect centering of the pistons in their cylinders generally leads in a relatively short time to the cylinders and pistons becoming oval, with a consequent drastic reduction in efficiency.